Pharmacokinetic models are developed for the distribution and disposition of drugs, environmental contaminants, and endogenous metabolites in animals and humans. They provide a plausible set of equations that can be used to extrapolate data from animals to humans, and thereby improve chemotherapy and risk assessment. Consideration of regional drug delivery includes intra-arterial infusion, intracavitary administration, and direct intratumoral infusion. Work is in progress on the development of a physiological pharmacokinetic model for methylmercury and inorganic mercury in the rat. work is also in progress on the adaptation of a pharmacokinetic model for cis-diamminedichloroplatinum(II) to other platinum-containing complexes. Increased emphasis has been placed on the pharmacokinetics of macromolecules, such as monoclonal antibodies and immunotoxins. Pharmacokinetics of alkylating agents used in cancer therapy provide a basis for correlating interspecies carcinogenicity.